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To improve both the stability and the disturbance suppression ability of single-phase grid-connected inverters through LCL filters, this paper proposes an inverter output impedance enhancing control mechanism. The impedance enhancing control mechanism employs a virtual impedance control and a node-voltage feedforward control to ensure sufficient passivity and high amplitude of inverter output impedance over wide frequency range of interest. The proposed control mechanism is realized through combination control of a low-voltage bidirectional voltage-source-converter (B-VSC) connected at the filter capacitor branch and the main inverter. The B-VSC sustains an extra low power without sacrificing the efficiency of the inverter. Both the simulation and experimental results are finally given to verify the validity of the proposed method, which shows the performance improvement of the proposed radial-line inverter system working under variable grid conditions.

In this article, the primary-side regulation (PSR) technique to achieve accurate output current in an LLC resonant converter has been studied. A novel PSR control scheme for an LLC light-emitting diode (LED) driver based on the “magnetizing current cancellation method” is proposed. The proposed “magnetizing current cancellation method” can effectively eliminate the effect of magnetizing current in the sampled primary resonant current under both the continuous conduction mode and the discontinuous conduction mode. Thus, the accurate output current can be estimated on the primary side of the LLC resonant converter. The magnetizing current cancellation method for the LLC LED driver with symmetric primary resonant current and asymmetric primary resonant current has been analyzed in detail. Some design considerations have also been presented. Then, an LLC PSR control circuit has been designed based on the theoretical analysis. Finally, a 48-to-78-V/1.3-A laboratory prototype for the LED driver has been built up, and experimental results show that good output current regulation has been obtained.

Nonlinear boundary control technique can offer superior dynamic behavior and eliminate the LCL-filter resonance in the grid-connected inverter. However, the chattering might be aroused by the distorted intracycle voltage information in the control law. It becomes worse when the nonlinear boundary controller is directly applied in three-phase three-wire inverter configuration. A hybrid current control scheme utilizing the decoupled predictive hysteresis capacitor current controller integrated with the linear grid current controller is proposed in the paper. By applying the 60° discontinuous pulse-width modulation scheme and using the virtual dual-buck decoupled structure, two separate sets of switching criteria for dictating the switching states of two specific half-bridge legs are formulated to avoid the interactions amongst phases. A small-signal ac model is also built to study the transfer characteristics of such hybrid current controlled inverter system. Simulation and experimental results have been offered to evaluate the effectiveness of the proposed method. Both results meet the theoretical predictions.

The resistor-capacitor-diode (RCD) level shift driving circuit takes advantages of low cost and tunable negative voltage level, therefore, it can satisfy the needs of drivers for various types of SiC MOSFETs easily. However, since the slow startup response of conventional RCD level shifter, it is not suitable for double pulse test (DPT). Furthermore, the conventional RCD level shifter does not consider the crosstalk problem caused by the high switching speed of SiC MOSFET in phase leg configuration. This paper introduces a novel high speed RCD level shift driving circuit. The proposed driving circuit has fast startup response to satisfy the needs of DPT. Moreover, in order to suppress the crosstalk, the snubber capacitors are added in the proposed driving circuit to reduce the impedance of the path for displacement current. Finally, the experimental results demonstrate the effectiveness of this proposed driving circuit.

Due to the existence of unknown grid impedance, the grid-connected inverter interacts with the grid and other distributed multiple paralleled inverters at the point-of-common-coupling (PCC). Such interaction challenges the system stability and the power quality especially when the inverter is with an LCL filter. A low-loss grid decoupling mechanism is proposed to counteract the effects of grid impedance in a three-phase grid connected inverter. It is composed of dual PCC voltage feedforward mechanisms, in which one is inserted at the inverter controller and the other is involved in the voltage regulation of an additional bidirectional dc/ac voltage source converter (B-VSC). The outputs of the B-VSC are connected in series with the ac filter capacitors while its inputs are provided with dc capacitors at the inverter dc bus. Because of small volt-ampere (VA) rating, the system efficiency is not sacrificed by the B-VSC. To validate its effectiveness, a three-phase inverter prototype with the proposed grid decoupling mechanism is verified successfully in the simulation.

To improve the stability of grid-connected inverter with an LCL filter, existing approaches are to reshape the inverter output impedance by damping filter resonance with passive or active damping methods. However, the interaction between the inverter and the grid still challenges the system performance especially when the grid becomes weak. This paper proposes an active compensator to counteract the effects of grid impedance on the stability of grid-connected inverter with an LCL filter. It is composed of dual unit PCC voltage feedforward mechanisms, wherein one is integrated into the inverter control, and the other is combined with a bidirectional dc/ac voltage source converter (B-VSC) in series at the filter capacitor branch. The power loss of the B-VSC is small and thereby the system efficiency is not sacrificed. To validate its effectiveness, a single-phase inverter prototype with the proposed compensator has been built.

A new primary side controlled high power factor single-stage flyback LED driver with self-adjusted current reference proposed in this paper. The self-adjusted current reference is realized by a negative feedback circuit to achieve output current regulation and suitable for discontinuous conduction mode (DCM) or boundary conduction mode (BCM). The output of the self-adjusted current reference is a half-sine waveform and followed by the primary current, hence high power factor can be achieved. A DCM single-stage flyback LED driver with self-adjusted current reference is analyzed in this paper and detailed design considerations are presented. Finally, a DCM laboratory prototype for LED driver with 360mA/25V output based on the theoretical analyses was built up. Experimental results show that good output current regulation and high PF can be achieved.

An optocouplerless two-stage high power factor LED driver is proposed in this paper. The first stage is an optocouplerless isolated PFC converter and the second stage is a constant-current controlled non-isolated DC/DC LED driver. Optocoupler and secondary amplifier circuit of the first PFC stage can be removed. Besides, the output capacitor s of the PFC stage can be reduced due to low output ripple voltage requirement and acceptable wide input voltage range of the secondary stage in the two-stage LED driver. Hence the circuit structure of the proposed optocouplerless two-stage high power factor LED Driver is much simplified. A prototype LED driver for 12W LED fluorescent tube is built up to verify theoretical analysis and experiment results are presented.